Faces with more than four vertices for 3D printing
You shouldn't use ngons for printing. Not even quads. Send triangulated mesh to the printer.

Ngons (and quads) are very convenient to work with. You can use knife tool on them easily. Because of this I would recommend using F when making the model.

For export for printing, use the Triangulate modifier and the Wire and Use All Edges option for Object Display. This allows you to control how the model will exactly triangulate and how it will print. You have more control over the triangulation and you can set the same Beauty algorithm for triangulating ngons as the Alt F command does by default.

Most exporters will allow you to apply modifiers on export, so you don't have to triangulate you model in Blender which makes it easier to do changes on the model later.